Problem: 3 glue sticks cost $4.74. Which equation would help determine the cost of 15 glue sticks?
Answer: There are several equations that could help determine the cost, each with a slightly different approach. We can write the fact that 3 glue sticks cost $4.74 as a proportion: $\dfrac{3}{\$4.74}$ Let $x$ represent the unknown cost of 15 glue sticks. Since 15 glue sticks cost $x$ , we have the following proportion: $\dfrac{15}{x}$ The cost changes along with the number of glue sticks purchased, and so the two proportions are equivalent. $\dfrac{3}{\$4.74} = \dfrac{15}{x}$